1. Field of the Invention
This invention relates to scaffolds and more particularly to self-raising scaffolds.
2. Background of the Prior Art
Conventional scaffolding has proven ineffective and very expensive for use on containment structures having cylindrical sides and a hemispherical roof. Such structures are being used to house nuclear reactors, and include a reinforced concrete structure consisting of a vertical cylinder, a hemispherical dome, and a flat foundation mat. For safety purposes containment structures for nuclear reactors are prestressed by a post-tensioning system and have a portion thereof below ground level. Vertical concrete buttresses are provided for anchoring horizontal tendons in the cylinder walls and part of the dome section. Scaffolding is utilized to provide access to the buttresses and install the tendons to prestress the structure.
It is known to suspend a scaffold from lines connected to the top of a vertical walled building and to raise and lower the scaffold by means of line grippers and climbers. It is also known to provide a scaffold with a plurality of long rollers whose axes lie in a plane inclined to the scaffold floor, whereby the scaffold can be operated over an inclined roof or wall. Neither of these systems is satisfactory for a dome shaped structure since the attitude of the wall of a dome changes from vertical to horizontal as one progresses from the springline to the apex of the dome.